Dental caries is one of the most prevalent diseases in the world and the development of a vaccine to protect populations against this ubiquitous malady has been the focus of a great deal of research. Nevertheless, despite the intense interest of the scientific community and in the face of successful vaccines for other infectious diseases, attempts to protect the experimental animals by immunization have only been partially successful. The purpose of the proposed investigation is to explore the possibility that the establishment of residence in the oral cavity by cariogenic bacteria leads to an active state of immunological tolerance and that attempts to immunize animals may actually be counterproductive. The experiments outlined herein will demonstrate that cariogenic bacteria, represented by Streptococcus mutans, establish themselves as commensal organisms in susceptible rodent hosts and that this commensal status leads to immunological events that affect the way the animals' immune systems respond to the bacteria. This study will try to identify the type of immune cells and cell products involved, the sites of activity, and the immune systems affected. The nature of the immune respose to enteric bacteria will be characterized using a radioimmunoassay (RIA) and an enzyme-linked immunosorbant-assay (ELISA). The nature of the cells involved in the depression of the response to commensal bacteria will be defined using the RIA assay for in vitro antibody synthesis. Armed with this information it is hoped that we may be able to suggest vaccination regimens that will preclude and/or circumvent the suppressive regulatory system to provide a useful tool with which to further protect people against dental caries.